Definition
A weather advisory issued for hazardous convective weather that is significant to all aircraft. A Convective SIGMET is issued for severe thunderstorms with surface winds of 50 knots or greater, hail at the surface 3/4 inch or greater in diameter, tornadoes, embedded thunderstorms, lines of thunderstorms, and thunderstorms covering 40 percent or more of an area of at least 3,000 square miles. Convective SIGMETs are issued for the contiguous 48 states only and are valid for 2 hours.
Plain English
An urgent weather alert about thunderstorms or related severe weather that is dangerous to every aircraft, no matter the size. It warns pilots about things like big thunderstorms, tornadoes, large hail, or thunderstorm lines.
Context Anchor
Pilots encounter Convective SIGMETs during preflight weather briefings, in aviation weather products, and in updated weather information while already en route.
Derivation
Convective' comes from the Latin 'convehere,' meaning 'to carry together.' In weather, convection refers to the rising and sinking of air that builds thunderstorms. So a Convective SIGMET is a significant meteorological warning specifically about thunderstorm-type weather.
Why Pilots Care
These advisories mark areas where severe weather can produce loss of aircraft control, structural damage, or rapid changes in flight conditions, requiring pilots to reroute or delay.
Grounding Statement
Picture warm, moist air rising quickly into a tall storm cloud; that rising air can produce violent air movement, lightning, heavy rain, and hail.
Intuition Check
A Convective SIGMET is not a routine rain forecast. It is an advisory for thunderstorm-related weather considered dangerous to every type of aircraft.
Example Sentence 1
During the preflight briefing, the pilot noted a Convective SIGMET for a line of thunderstorms along the planned route and decided to delay departure.
Example Sentence 2
ATC relayed an updated Convective SIGMET that now included the destination airport, prompting the crew to divert.